Senate Democrats demanded that oil company executives who testified last week about skyrocketing energy prices reappear before lawmakers and testify under oath, after news reports raised questions about the truthfulness of their testimony.

Leading oil company executives long have denied taking part in a secretive energy task force run in 2001 by Vice President Dick Cheney, but White House records obtained by The Washington Post refuted that, according to the daily's editions on Wednesday.

The ad hoc group was tasked with helping develop a national energy policy, but was opposed by environmentalists because there allegedly were no ecologically friendly players on the panel.

The leader of Senate Democrats said the oil company executives who testified last week should be forced to return to Congress to set the record straight regarding their involvement with Cheney's group.

'When the big oil companies came to Congress to testify about their record profits, we expected that they would tell the whole truth and nothing but the truth. Today, we learned that this was a standard they were not prepared to meet,' said Senator Harry Reid.

Democrats also objected to a decision by the leaders of the Republican-led Senate to waive swearing in the witnesses. At any future hearing, Reid said, the executives should testify under oath.

Meanwhile, Democratic Senator Frank Lautenberg called at a press conference for an investigation.

'I want to be certain that this gets an appropriate review, so I've written to the attorney general asking him to investigate whether any of these oil company CEOs broke the law by making false statements to the Congress,' Lautenberg said.